Field of the Invention
Embodiments of the invention generally relate to stop collars for use on a wellbore tubular.
Description of the Related Art
A wellbore is formed to access hydrocarbon bearing formations, such as crude oil and/or natural gas, by the use of drilling. Drilling is accomplished by utilizing a drill bit that is mounted on the end of a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on a surface platform or rig, and/or by a downhole motor mounted towards the lower end of the drill string. After drilling to a predetermined depth, the drill string and drill bit are removed and a casing string is lowered into the wellbore. An annulus is formed between the string of casing and the wellbore. The casing string is cemented into the wellbore by circulating cement slurry into the annulus. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain formations behind the casing for the production of hydrocarbons.
Centralizers are mounted on the casing string to center the casing string in the wellbore and obtain a uniform thickness cement sheath around the casing string. Multiple centralizers are spaced apart along the casing string to provide centralization of the casing string at multiple points throughout the wellbore. Each centralizer has blades extending out from the casing wall and contacting the wellbore, thereby holding the casing string off of direct contact with the wellbore wall, and substantially centralizing the casing therein. To accomplish that goal, the centralizer blades typically form a total centralizer diameter roughly the diameter of the wellbore in which the casing string is run.
One type of centralizer has a solid central tubular body having a plurality of solid blades integral with the central body, the blades extending out to the desired diameter. Another type is a bow spring centralizer having a pair of spaced-apart bands locked into place on the casing, and a number of outwardly bowed, resilient bow spring blades connecting the two bands and spaced around the circumference of the bands. The bow spring centralizers are capable of at least partially collapsing as the casing string passes through any restricted diameter location, such as a piece of equipment having an inner diameter smaller than the at-rest bow spring diameter, and then springing back out after passage through the restricted diameter location.
Stop collars are mounted on the casing string to restrict longitudinal movement of the centralizer on the casing string. A stop collar mounted above the centralizer on the casing string restricts upward movement of the centralizer while lowering the casing string into the wellbore. Likewise, a stop collar mounted below the centralizer on the casing string restricts downward movement of the centralizer while lifting the casing string in the wellbore. Conventional stop collars may catch and interfere with a wall of the wellbore in restricted diameter locations. Conventional stop collars may also require fasteners to attach to a casing string. Fasteners, such as screws, may scratch and damage an outer surface of the casing string. Conventional stop collars may also require measurement of each section of the casing string and custom manufacturing to ensure a suitable fit between the stop collar and the casing string. Because stop collars are mounted to the exterior of the casing string, the stop collar adds to the overall outer diameter of the casing string. There is a need for stop collars having a low profile to pass through restricted diameter locations in the wellbore, stop collars which can accommodate for variances in sections of the casing string, and different methods for attaching stop collars to prevent damaging the casing string.